The invention relates to an electronic pitch testing apparatus for gears.
Such apparatus is known comprising a probe unit having two stylus heads arranged side-by-side on a slide and which in one end position of the slide engage simultaneously in different tooth spaces of a gear and, because of a deflection produced by bearing against the tooth flanks, each produce, via a transmitter, electrical signals from which a signal for controlling the drive of the slide and a measurement value corresponding to the relative single pitch error are derived and recorded. One example of such apparatus is to be found in U.S. Pat. No. 2,906,030.
In the apparatus described there, the spacing of the stylus heads is initially so adjusted manually with the test element or gear stationary that both stylus heads bear against one tooth flank. A slow, constant rotation is then imposed on the test element. With each measurement and at the instant in which the one signal transmitter indicates a theoretical or rated value, a datum is established from the signal value indicated at the same instant by the other signal transmitter. The moment at which the rated value appears is further employed for initiating the movement of the slide. The speed of movement of the slide, which automatically reverses at its rearward end position and stops automatically in its forward end position in which the stylus heads extend into the gear tooth spaces, is adapted manually by way of a potentiometer to the speed of rotation of the test element.
With this and other known pitch testing apparatus, the establishment of the relative cumulative pitch error involves considerable difficulties, because, for this purpose, the initial setting of the spacing of the stylus heads must be as accurately as possible equal to the actual means value of the pitch on the circle probed by the apparatus. Otherwise, high relative cumulative pitch errors can be produced after a few separate measurements, such that these errors exceed the range of measurement of the testing instrument being used or the recording range of the recorder. The initial setting of the stylus heads would then have to be corrected, and the test series begun again.
A further characteristic of such known pitch testing apparatus is that other gear defects, such as maximum pitch overlap length and absolute cumulative pitch error, cannot be recorded at all or only after tedious evaluating operations. Furthermore, the apparatus contains an extensive group of instruments, which can only with difficulty be arranged on the gear machine itself.